FINGERPRINTS COLLEGE FORENSICS WHAT ARE FINGERPRINTS A fingerprint

FINGERPRINTS COLLEGE FORENSICS

WHAT ARE FINGERPRINTS? ? ? A fingerprint is an impression of the friction ridges found on the inner surface of a finger or a thumb

Cross-Section of Friction Skin *Subcutaneous (hypodermis) -Lowest layer *Dermis – Middle layer -protein *Epidermis – Outer layer An injury must penetrate the dermal layer to alter a print.

1) Ridge patterns and the details in small areas of friction ridges are unique and never repeated. 2) Friction ridges develop on the fetus between the 3 rd and 5 th month of prenatal development. The dermal papillae determines the pattern. *Ridges are persistent throughout life except for permanent scarring. 3) Friction ridges increase the surface area of the fingertip and hands to assist in gripping items.

RIDGES & FURROWS Ridges – top of the ‘hill’ Furrows – Lower ‘valleys’

FINGERPRINT PATTERNS: Arch *Ridges enter & exit from opposite sides. *Found on approx. 5% of the population *No deltas, no core Plain Arch Tented Arch: Smaller angle at top of arch

FINGERPRINT PATTERNS: Loop *Ridge enters & exits from the same side *Found in 60 -70% of the population *1 Delta (point where 3 ridges converge) & 1 Core *Loops are classified as radial or ulna, depending on which direction it opens towards.

Direction changes with right vs. left hand

FINGERPRINT PATTERNS: Whorl *Completes a 360 o pattern *Found in 25 -30% of population *2 Deltas, 1 Core *Many forms of whorls: -Plain whorl -Central pocket -Double loop -Accidental

FINGERPRINT PATTERNS: Whorls Central Pocket Loop Double Loop Accidental

Levels of Detail What are three levels of detail in a fingerprint? ? ? Structure (type of pattern) 2) Individual minutae/friction pattern 3) Detail of ridge measurement (width, length, distance between minutae) 1)

FINGERPRINT MINUTIAE WHAT MAKES ONE PERSON’S FINGERPRINT DIFFERENT FROM ANOTHER PERSON’S? There are small patterns and designs that are present on the ridge pattern of your fingertips. These small differences make fingerprints unique.

TYPES OF MINUTIAE Dot: Bifurcation: Trifurcation: Lake/ Enclosure:

Minutae Ridge Ending: Island/Short Ridge: *A short ridge doesn’t travel through the entire pattern; It is only a few millimeters in real size.

Minutae Break: Island: Hook: Bridge:

Let’s Look at this print…

MINUTIAE TYPE OF PATTERN: Arch UNIQUE CHARACTERISTICS: *Lake *Bifurcation *Island *Ridge Ending *Break

RIDGE COUNT The number of ridges crossed between a delta and the core of the pattern. *Can only be done on loops & whorls. *Whorls will have a right ridge count & a left ridge count.

Primary Classification A numerical system of classifying a full set of prints based on the whorl pattern. *Numerical values are assigned to each finger *If the finger has a whorl pattern, then plug that number into the primary classification equation. *If a whorl is not present, use ‘ 0’ as that finger’s value *Final classification is NOT reduced & left in the fraction form.

PRIMARY CLASSIFICATION (Henry Classification System) NUMBERS ASSIGNED IF A WHORL IS PRESENT: Fingers #1, 2 = 16 Fingers #3, 4 = 8 Fingers #5, 6 = 4 Fingers #7, 8 = 2 Fingers # 9, 10 = 1 EQUATION = (Sum of #’s assigned to even numbered fingers) +1 (Sum of #’s assigned to odd numbered fingers) +1 *Practice Problems

PRIMARY CLASSIFICATION (Henry Classification System) Therefore, a person with whorl patterns on all of their fingers would have a Primary Classification of 32 32 And a person with no whorl patterns on any of their fingers would have a Primary Classification of 1 1 These ratios are not to be reduced, they are to be left as calculated.

SECONDARY CLASSIFICATION Fraction of index finger patterns: Right Index Pattern Left Index Patterns: Arch = A Tented Arch = T Ulna L. = U Radial L. = R Whorl = W (any whorl pattern) Example: A/T (right index has an arch, left index has a tented arch)

DEVELOPING FINGERPRINTS Types of fingerprints: 1)Latent – Impressions caused by oils, water, amino acids (perspiration) left on a surface 2)Visible Prints – Left when ridges have a colored/medium substance on them 3)Impression Prints – ‘Plastic’ prints left in a soft material

DEVELOPING FINGERPRINTS DEVLOPING FINGERPRINTS DEPENDS ON… 1) SURFACE THE PRINT IS ON *Porous (Absorbent) *Non-porous (nonabsorbent) 2) METHODS FOUND SUCCESSFUL BY DEVELOPER

DEVELOPING FINGERPRINTS: Nonabsorbent surfaces 1) Powder – Adheres to body oils, perspiration. -Color used depends on background. -Lift with tape, place on card. Print card contains information of the suspect (name, DOB, age, height, weight)

DEVELOPING FINGERPRINTS: Nonabsorbent surfaces Developing Latent Prints on Nonabsorbent Surfaces 2) Reflected UV Imagining System (RUVIS) - UV light strikes print and reflects back to a viewer that is converts it to visible light.

DEVELOPING FINGERPRINTS: Nonabsorbent surfaces 3) Superglue Fuming – Fumes react with amino acids and make it white. -Cyanoacrylate ester is the chemical that interacts with the print. -Superglue is heated to produce a vapor. -Can be used on small objects or cover a large area (car interior)

DEVELOPING FINGERPRINTS: Absorbent surfaces 1) Iodine Fuming – Iodine fumes combine with fatty oils / water -Iodine sublimes (solid gas) -Not a permanent image

DEVELOPING FINGERPRINTS: Absorbent surfaces 2) Ninhydrin – Chemical treatment; reacts with amino acids in perspiration. -Sprayed onto surface; 1 -2 hours to develop. -Produces purple-blue print -Last for 24 -48 hours

DEVELOPING FINGERPRINTS: Absorbent surfaces 3) Silver-nitrate (Physical developer) – Solution reacts with chloride ions in sweat but washes away any trace of protein left on print. -Last resort for developers - May detect prints on porous objects that may have been wet @ one point.

Order of Chemical Treatments Since some chemical treatments are more destructive than others, the treatments must be performed in the following order… 1) Iodine fuming 2) Ninhydrin 3) Silver nitrate

VISUALIZING FINGERPRINTS *Alternate Light Source (ALS) – Specific wavelengths of light aimed at a print; Based off of fluorescent tendencies of chemically treated prints. (Previously done with lasers) -Cheaper than lasers -Portable, easy to use -Used with chemical treatments

DEVELOPING FINGERPRINTS

PRESERVATION OF PRINTS After visualization, prints must be permanently preserved At Crime Scene photograph first (Close-up of print and relationship to evidence) Object collected or print lifted from large objects. *Prints are lifted by placing cellophane tape over a dusted print.

PRESERVATION OF PRINTS DIGITAL IMAGING – Computer programs used to enhance photos of prints *Filters used to make print clearer (Grayscale, contrast, interference) *Colors can be differentiated (print on a dollar bill or colored background) *’Compare’ function – side-by-side comparison.